In order to expand the thioester method, we searched the route for the preparation of S-proted two methods for the preparation of S-protected peptide thioesters via low- or high-HF treatment of protected peptide resins obtained by Boc strategy of a solid-phase method. This year, a more efficient method for the preparation of S-protected peptide thioester wwas developed. In this method, peptide chain was elongated by using Npys-amino acids. A cysteine residue is introduced by Npys-Cys(Tmb) (Tmb : 2,4,6-trimethylbenzyl). Aprotected peptide resin was treated by reagent K to give an S-protected peptide thioester. The Tmb group on the mercapt group was stable during reagent K treatment and segment condensation.Vased on this preparation strategy, cysteine-containing peptide thioesters were synthesized and used for the syntheses of the barmase-like domain ( 112 amino acid residues) in DNA-directed RNA polymerase II of Saccharomyces cerevisiae (RPSc(299-410)). RPSc(299-410) was successfully synthesided. This strateby was also applied to the preparation of tAT protein of HIV-1, which has 7 cysteine residues, was also synthesized by the thioester method. the interaction between TAT protein and zinc ions is now under investigation.To conclude, the thioester method can be applied to the synthsis of proteins with cysteine residues as sell as without them.本研究により、チオエステル法をシステイン含有蛋白質の合成にも適用することが可能となった。